The purpose of this project is to study cholesterol metabolism in human monocyte-derived macrophages, a major cell that accumulates cholesterol in atherosclerotic lesions. Also, because cholesterol accumulates predominantly in macrophages in genetically determined cholesterol storage diseases, we plan to use cultured human monocyte-derived macrophages from patients with these diseases to investigate possible cellular abnormalities in lipoprotein and cholesterol processing in these diseases. When normal monocyte-derived macrophages were incubated with low density lipoprotein, macrophages accumulated unesterified cholesterol (15 nM/mg protein) but did not accumulate triglycerides and usually no cholesteryl ester. Addition of albumin (0.35%) potentiated the accumulation of unesterified cholesterol by macrophages. When normal monocyte-derived macrophages were incubated with very low density lipoprotein (VLDL), macrophages accumulated triglycerides but did not accumulate cholesteryl ester. Triglyceride accumulation in normal monocyte-derived macrophages increased proportionately with increasing concentrations of VLDL. Accumulation of triglycerides by macrophages incubated with VLDL did not depend on the presence of serum. When macrophages were incubated with VLDL at total cholesterol concentrations below and above 150 nM/ml, cellular unesterified cholesterol content decreased. VLDL added at a concentration of 150 nM/ml stimulated cholesterol accumulation of unesterified cholesterol. When macrophages were incubated with 50% or 100% human serum total cellular cholesterol content decreased 28% and 45%, respectively. Because macrophages are one of the major types of cells which accumulate cholesterol in atherosclerotic lesions, it is of great significance to develop an in vitro model to study their cholesterol metabolism. By incubating these cells with lipoprotein and non-lipoprotein cholesterol forms, we will be able to examine pathways of cholesterol metabolism in macrophages from normal individuals and patients with cholesterol storage diseases.